1. Field of the Invention
A lens device is provided that is not affected by changes in environmental conditions and is capable of manual and automatic focussing. Specifically, using a simple structure, the lens device generates an appropriate operational load during automatic or motor driven operations and manual operations of the lens device.
2. Description of Related Art
Many conventional lens devices adjust the focus by manually moving the lens contained within the lens barrel. Cameras, for example, use such lens focusing devices. These types of lens devices are usually equipped with an operation ring around the outer periphery of the lens barrel. By rotating the operation ring, the lens in the lens barrel moves in a known manner. In addition, a high viscosity lubricating oil is applied to all lens barrel sliding parts to reduce friction. However, the operation ring is preferably designed to retain a limited amount of friction. While rotating the operation ring, the limited friction causes an appropriate operational load. During lens barrel use, the appropriate operational load improves fine-tuning of the focus and provides a high-quality feel to the user.
However, lubricating oil viscosity varies considerably with temperature. In other words, the lens barrel operational load of the camera changes between high temperature and low temperature use. Further, user survey results indicate in situations of extreme heat or severe cold, the environment is suspected of inadvertently influencing the rotation of the operation ring itself.
There are variations or ranges in the operational load, that feels most comfortable to individual photographers. Further, depending upon where the camera is used, there are situations where the user finds changing the operational load desirable. In other words, having the operational load of the operation ring freely adjustable by the photographer may be beneficial.
A lens device for cameras that selectively adjusts the lens movement using a lens drive device and manual lens movement is well known in the art. Such a conventional lens device for cameras, for example, is shown in FIG. 10.
In FIG. 10, a lens device 40 for cameras includes a lens holding barrel 2 holding a lens 1, and a cam-follower 5 protrudes from the lens holding barrel 2 periphery. A lens barrel 3 holds the lens holding barrel 2 through the cam-follower 5. An operational ring 6 is rotatably mounted at the periphery of the lens barrel 3. A lens drive device 41 rotates the operation ring 6. The central part of the cam-follower 5 is slidingly inserted into an optical axis direction channel 4 provided at the circumference partition of the lens barrel 3. The optical axis direction channel 4 is substantially parallel to the optical axis direction. The tip part of the cam-follower 5 is slidingly inserted into a non-optical axis direction cam channel 7 provided at the circumference partition of the operation ring 6. The non-optical axis direction channel 7 is substantially perpendicular to the optical axis direction. The lens drive device 41 also includes a motor 13, a motor drive circuit 14 that drives the motor 13, a switch 42, and a deceleration device 11. The deceleration device 11 includes a gear 12 that intermeshes with a gear 9 located at the periphery of the operation ring 6.
The lens device 40 enables manual focussing of the lens or through the lens drive device 41 automatic focussing of the lens. The photographer connects the switch 42 to the motor drive circuit 14 to automatically rotate the operation ring 6 through lens drive device 41. When switch 42 is connected, the motor drive circuit 14 drives the motor 13, which through the deceleration device 11 rotates the operation ring 6. During manual operations, switch 42 is opened, and the operation ring 6 is rotated by hand. When the operation ring 6 is rotated, the cam-follower 5 correspondingly moves along channel 4 in the direction of the optical axis in a known manner. The cam-follower 5 travel direction is reversible according to the rotational direction of the operation ring 6. Therefore, the lens 1 moves reversibly with the lens holding barrel 2 along the optical axis without rotating inside the lens barrel 3.
However, in conventional lens devices as shown in FIG. 10, the motor load is preferably the smallest amount possible to improve the accuracy of the position control and the drive speed of the motor 13 in the lens drive device 41. To reduce the motor load, for example, the friction resistance of the lens movement mechanisms can be reduced by allowing play in the pressed-in parts of the cam-follower 5.
The friction resistance cannot be reduced beyond a minimal amount or a problem occurs when the lens barrel 3 is tipped and the lens holding barrel 2 inside spontaneously moves merely because of the weight of the lens 1. When the lens barrel moves, the operation ring 6 rotates. Under these conditions, providing the appropriate operational load during manual operations is unobtainable.
To handle such disparate conditions, prior art lens devices either prioritized motor drive focussing using a minimal motor load, and thereby during manual operations the operational load was less than optimal. Alternatively, the prior art lens devices prioritized manual operation focussing by increasing the friction resistance, and thereby increased the motor operational load beyond optimal limits.
To solve these problems, one prior art lens drive devices includes a viscosity resistance generation device. During manual operations, the viscosity resistance generation device provides an acceptable operational load through viscosity fluid viscosity resistance. Then, during motorized operations, the viscosity resistance generation device is bypassed and the motor drives the lens under an optimal low load condition.
However, the viscosity resistance generation device has a complicated structure and assembly. Additionally, when mechanisms are provided to freely adjust the operational load, the viscosity resistance generation device becomes even more complicated. Further, the viscosity fluid enclosed inside the camera complicates maintenance, and possible fluid leaks present potentially severe damage hazards.